The old (5.7) 350 Oldsmobile diesel engines found in the Oldsmobiles, the Cadillacs and the Chevrolet trucks had head bolts like you need. The General Motors part number is number: Gr. (Group) 0.293 Part Number 022520637. This is actually a 3 inch long head bolt with a stud on top from the diesel engine that will work as a head bolt on a 216-235-261 head. You might check with a parts counter at one of those General Motors dealerships. I used them on my 261. The wrench size is one size larger, but they work perfectly.
Good luck!
Joe
